Staphylococcus aureus 
Staphylococcus aureus (“S. aureus”) is a bacterium that commensally colonizes more than 25% of the human population. Importantly, this organism is capable of breaching its initial site of colonization, resulting in bacterial dissemination and disease. S. aureus is the leading cause of nosocomial infections, is the most common etiological agent of infectious endocarditis as well as skin and soft tissue infections, and is one of the four leading causes of food-borne illness. Altogether, S. aureus infects more than 1.2 million patients per year in U.S. hospitals. The threat of S. aureus to human health is further highlighted by the emergence of antibiotic-resistant strains (i.e., methicillin-resistant S. aureus (MRSA) strains), including strains that are resistant to vancomycin, an antibiotic considered the last line of defense against S. aureus infection. These facts highlight the importance of developing novel therapeutics against this important pathogen.
S. aureus produces a diverse array of virulence factors and toxins that enable this bacterium to neutralize and withstand attack by different kinds of immune cells, specifically subpopulations of white blood cells that make up the body's primary defense system. The production of these virulence factors and toxins allow S. aureus to maintain an infectious state (Nizet, “Understanding How Leading Bacterial Pathogens Subvert Innate Immunity to Reveal Novel Therapeutic Targets,” J. Allergy Clin. Immunol. 120(1):13 22 (2007)). Among these virulence factors, S. aureus produces several bi-component leukotoxins, which damage membranes of host defense cells and erythrocytes by the synergistic action of two non-associated proteins or subunits (see Menestrina et al., “Mode of Action of Beta-Barrel Pore-Forming Toxins of the Staphylococcal Alpha-Hemolysin Family,” Toxicol. 39(11):1661-1672 (2001)). Among these bi-component leukotoxins, gamma-hemolysin (HlgAB and HlgCB) and the Pantone-Valentine Leukocidin (PVL) are the best characterized.
The toxicity of the leukocidins towards mammalian cells involves the action of two components. The first subunit is named class S-subunit (i.e., “slow-eluted”), and the second subunit is named class F-subunit (i.e., “fast-eluted”). The S- and F-subunits act synergistically to form pores on white blood cells including monocytes, macrophages, dendritic cells and neutrophils (collectively known as phagocytes) (Menestrina et al., “Mode of Action of Beta-Barrel Pore-Forming Toxins of the Staphylococcal Alpha-Hemolysin Family,” Toxicol. 39(11):1661 1672 (2001)). The mechanism by which the bi-component toxins form pores in target cell membranes is not entirely understood. The proposed mechanism of action of these toxins involves binding of the S-subunit to the target cell membrane, most likely through a receptor, followed by binding of the F-subunit to the S-subunit, thereby forming an oligomer which in turn forms a pre-pore that inserts into the target cell membrane (Jayasinghe et al., “The Leukocidin Pore Evidence for an Octamer With Four LukF Subunits and Four LukS Subunits Alternating Around a Central Axis,” Protein. Sci. 14(10):2550 2561 (2005)). The pores formed by the bi-component leukotoxins are typically cation-selective. Pore formation causes cell death via lysis, which in the cases of the target white blood cells, has been reported to result from an osmotic imbalance due to the influx of cations (Miles et al., “The Staphylococcal Leukocidin Bicomponent Toxin Forms Large Ionic Channels,” Biochemistry 40(29):8514 8522 (2001)).
Designing effective therapy to treat MRSA infection has been especially challenging. In addition to the resistance to methicillin and related antibiotics, MRSA has also been found to have significant levels of resistance to macrolides (e.g., erythromycin), beta-lactamase inhibitor combinations (e.g., Unasyn, Augmentin) and fluoroquinolones (e.g. ciprofloxacin), as well as to clindamycin, trimethoprim/sulfamethoxisol (Bactrim), and rifampin. In the case of serious S. aureus infection, clinicians have resorted to intravenous vancomycin. However, there have been reports of S. aureus resistance to vancomycin. Thus, there is a need to develop new antibiotic drugs that effectively combat S. aureus infection.
C—C Chemokine Receptor Type 5
C—C chemokine receptor type 5 (CCR5) is a member of the beta chemokine receptors family (Samson M et al., “Molecular Cloning and Functional Expression of a New Human CC-Chemokine Receptor Gene” Biochemistry 35:3362 (1996)). The normal ligands for this receptor are RANTES, Mip1b, and Mip1a (see Samson, supra and Gon W et al “Monocyte Chemotactic Protein-2 Activates CCR5 and Blocks CD4/CCR5 Mediated HIV-1 Entry/Replication,” J. Biol. Chem. 273:4289 (1998)). CCR5 is expressed on a subset of T cells, macrophages, dendritic cells, natural killer cells, and microglia. CCR5+ T cells secrete pro-inflammatory cytokines and are recruited to sites of inflammation. Thus, it is likely that CCR5 plays a role in inflammatory responses to infection and in pathological conditions such as autoimmune diseases. CCR5 is also the receptor for major strain of HIV (Deng H et al., “Identification of a Major Co-Receptor for Primary Isolates of HIV-1,” Nature 381:661-666 (1996)). In individuals infected with HIV, CCR5-using viruses are the predominant species isolated during the early stages of viral infection, suggesting that these viruses may have a selective advantage during transmission or the acute phase of disease. Moreover, at least half of all infected individuals harbor only CCR5-using viruses throughout the course of infection. Around 1% of Northern Europeans lack functional CCR5 expression, due to a 32 base pair deletion in this gene. Individuals with the Δ32 allele of CCR5 are healthy, suggesting that CCR5 is largely dispensable. However, these individuals have very strong resistance to HIV infection (Liu R et al., “Homozygous Defect in HIV-1 Coreceptor Accounts for Resistance of Some Multiply-Exposed Individuals to HIV-1 Infection,” Cell 86:367-377 (1996)). Indeed, an AIDS patient who had myeloid leukemia was treated with chemotherapy to suppress the cancer, which killed all of his T cells. The patient was then transplanted with a donor blood that had the 32 bp CCR5 deletion mutant to restore the immune system. After 600 days, the patient was healthy and had undetectable levels of HIV in the blood and in examined brain and rectal tissues (Witter G et al., “Long-Term Control of HIV by CCR5 Delta32/Delta32 Stem-Cell Transplantation,” N. Engl. J. Med. 360:692-698 (2009)). A number of new experimental HIV drugs, called entry inhibitors have been designed to interfere with the interaction between CCR5 and HIV, including PRO140, Vicriviroc, Aploviroc, and Maraviroc (Pfizer), of which the latter is currently an approved drug for HIV infection.
CCR5 is also involved in uncontrolled inflammation (Charo et al., “The Many Roles of Chemokine Receptors in Inflammation,” N. Engl. J. Med. 354:610-621 (2006)). This association is based on the role of this chemokine receptor in the recruitment of inflammatory leukocytes. In particular, CCR5 is expressed in a subset of effector T cells that produce proinflammatory cytokines such as interferon gamma (IFNg) and interleukin-17 (IL-17), which are enriched locally during inflammation. Thus, CCR5 is being considered as a target to dampen inflammatory disorders, such as rheumatoid arthritis (RA), Crohn's Disease (CD), atherosclerosis, and psoriasis among others.
The present invention is directed to overcoming these and other limitations in the art.